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<h1 class="lined-header"><span>cowboy_req:match_qs(3)</span></h1>
<div class="sect1">
<h2 id="_name">Name</h2>
<div class="sectionbody">
<div class="paragraph"><p>cowboy_req:match_qs - Match the query string against constraints</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">Description</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #000000">match_qs</span></span>(<span style="color: #009900">Fields</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">cowboy:fields</span></span>(), <span style="color: #009900">Req</span> <span style="color: #990000">::</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:req</span></span>())
<span style="color: #990000">-></span> #{<span style="font-weight: bold"><span style="color: #000080">atom</span></span>() <span style="color: #990000">=></span> <span style="font-weight: bold"><span style="color: #000000">any</span></span>()}</tt></pre></div></div>
<div class="paragraph"><p>Parse the query string and match specific values against
constraints.</p></div>
<div class="paragraph"><p>Cowboy will only return the query string values specified
in the fields list, and ignore all others. Fields can be
either the key requested; the key along with a list of
constraints; or the key, a list of constraints and a
default value in case the key is missing.</p></div>
<div class="paragraph"><p>This function will crash if the key is missing and no
default value is provided. This function will also crash
if a constraint fails.</p></div>
<div class="paragraph"><p>The key must be provided as an atom. The key of the
returned map will be that atom. The value may be converted
through the use of constraints, making this function able
to extract, validate and convert values all in one step.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_arguments">Arguments</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
Fields
</dt>
<dd>
<p>
Fields to retrieve from the query string.
</p>
<div class="paragraph"><p>See <a href="../cowboy">cowboy(3)</a> for a complete description.</p></div>
</dd>
<dt class="hdlist1">
Req
</dt>
<dd>
<p>
The Req object.
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_return_value">Return value</h2>
<div class="sectionbody">
<div class="paragraph"><p>Desired values are returned as a map. The key is the atom
that was given in the list of fields, and the value is the
optionally converted value after applying constraints.</p></div>
<div class="paragraph"><p>The map contains the same keys that were given in the fields.</p></div>
<div class="paragraph"><p>An exception is triggered when the match fails.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_changelog">Changelog</h2>
<div class="sectionbody">
<div class="ulist"><ul>
<li>
<p>
<strong>2.0</strong>: Function introduced.
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_examples">Examples</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="title">Match fields</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900">%% ID and Lang are binaries.</span></span>
#{<span style="color: #FF6600">id</span> <span style="color: #990000">:=</span> <span style="color: #009900">ID</span>, <span style="color: #FF6600">lang</span> <span style="color: #990000">:=</span> <span style="color: #009900">Lang</span>}
<span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:match_qs</span></span>([<span style="color: #FF6600">id</span>, <span style="color: #FF6600">lang</span>], <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Match fields and apply constraints</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900">%% ID is an integer and Lang a non-empty binary.</span></span>
#{<span style="color: #FF6600">id</span> <span style="color: #990000">:=</span> <span style="color: #009900">ID</span>, <span style="color: #FF6600">lang</span> <span style="color: #990000">:=</span> <span style="color: #009900">Lang</span>}
<span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:match_qs</span></span>([{<span style="color: #FF6600">id</span>, <span style="color: #FF6600">int</span>}, {<span style="color: #FF6600">lang</span>, <span style="color: #FF6600">nonempty</span>}], <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
<div class="listingblock">
<div class="title">Match fields with default values</div>
<div class="content"><!-- Generator: GNU source-highlight
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>#{<span style="color: #FF6600">lang</span> <span style="color: #990000">:=</span> <span style="color: #009900">Lang</span>}
<span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:match_qs</span></span>([{<span style="color: #FF6600">lang</span>, [], <span style="color: #990000"><<</span><span style="color: #FF0000">"en-US"</span><span style="color: #990000">>></span>}], <span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">See also</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="../cowboy_req">cowboy_req(3)</a>,
<a href="../cowboy_req.qs">cowboy_req:qs(3)</a>,
<a href="../cowboy_req.parse_qs">cowboy_req:parse_qs(3)</a></p></div>
</div>
</div>
</div>
<div class="span3 sidecol">
<h3>
Cowboy
2.3
Function Reference
</h3>
<ul>
<li><a href="/docs/en/cowboy/2.3/guide">User Guide</a></li>
<li><a href="/docs/en/cowboy/2.3/manual">Function Reference</a></li>
</ul>
<h4 id="docs-nav">Navigation</h4>
<h4>Version select</h4>
<ul>
<li><a href="/docs/en/cowboy/2.4/manual">2.4</a></li>
<li><a href="/docs/en/cowboy/2.3/manual">2.3</a></li>
<li><a href="/docs/en/cowboy/2.2/manual">2.2</a></li>
<li><a href="/docs/en/cowboy/2.1/manual">2.1</a></li>
<li><a href="/docs/en/cowboy/2.0/manual">2.0</a></li>
<li><a href="/docs/en/cowboy/1.0/manual">1.0</a></li>
</ul>
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